Multiaxial Ferroelectricity and Ferroelasticity in a Chiral Perovskite

Organic–inorganic
lead-iodide perovskites are attracting
tremendous interest because of their great application potential in
optoelectronics and photovoltaics. Despite extensive interest, however,
no lead-iodide perovskites have been found as multiaxial multiferroic
materials with the coexistence of full ferroelectricity and full ferroelasticity.
Here, based on the ferroelastic [EQ]­PbI3 (EQ = N-ethyl-quinuclidine) with an Aizu notation of 6/mmmF2/m, we introduced a hydroxyl group
to N-ethyl-quinuclidine and successfully synthesized
a homochiral lead-iodide perovskite multiaxial multiferroic [(R)-N-ethyl-3-quinuclidinol]­PbI3 ([R-EQ]­PbI3). [R-EQ]­PbI3 undergoes a phase transition at 380 K from 622 to 2 point
groups, and thereby it is a multiaxial full ferroelectric and also
a multiaxial full ferroelastic in the room-temperature phase according
to the Aizu notation of 622F2(s). Multiple equivalent
ferroelectric/ferroelastic axes can endow [R-EQ]­PbI3 with a larger polarization/strain in the polycrystalline
samples. This work presents the first multiaxial full multiferroic
in lead-iodide perovskites, which would inspire further exploration
of chiral perovskite multiferroics for applications such as high precision
microdisplacement devices and variable surface acoustic wave delay
lines.